E-mail not working

I have a dedicated server managed by another hosting company, on the 24th of Decemeber they did some updates (mainly PHP 4.3.10, Zend, kernel. I think), everything went from bad to worse and there was about 9 hours downtime. Since then I'm not receiving external mail on any domain hosted on the server, the only mail the does come through are messages sent from the same server (cronjob messages, PHP mail(), etc). I sent a test message from my Gmail account and got this the next day: